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My understanding of the English language isn't complete, but I understood "theoretical physicists" to mean that the physicists themselves were only theoretical -- in much the same way that "garden gnome" is a gnome that lives in a garden.

Dude! Like, when you are hammered you can SEE it, right? The rest of the time nobody notices because they are out of sync with the universe! We are totally getting a Nobel Prize for this, but we're going to need enough booze to get the whole committee wasted so they can grasp the cosmic significance! And then enough Bloody Mary mix and vodka so they can write the proclamation (and the check) the next day...

Everything is science is "theoretical", that doesn't mean it's unlikely to be true.

Dark matter explains both galaxy rotation and the behavior of the early universe quite well. Until the CMBR data, dark matter was just one hypothesis among many for galaxy rotation, but only dark matter explained the observed pattern of mass distribution when the universe cooled enough to become transparent for the first time. And the numbers matched to a couple of significant digits, not in some hand-wavey way.

What dark matter is made of is still an open question, but it's pretty clear that about 4/5ths of the matter in the universe is dark.

It's not non science. Perhaps you should read "dark" as "unknown" instead. It's unknown energy, and unknown matter. It's just a place holder for something we don't yet understand. The scientists are fully aware it is something they don't understand. So they're not just making shit up.

There is evidence for dark matter from many areas of astronomy. Others have listed observational evidence and provided links to details. Follow them. I am not going to do your homework for you. Simply saying that something does not exist because you do not understand it, or because you do not want it to exist, or because you have a grudge against science is magical thinking.

There are decades of observational evidence that support the existence of dark matter. If you have any evidence that those observations are wrong, or have been interpreted incorrectly then feel free to present that evidence. You are making an extraordinary claim, that many years of research is wrong. You now need to provide evidence to back up your claim.

On the contrary. The only evidence we have is that it cannot yet be observed. Thus the moniker of being dark.

We can observe that there must be something there (from the gravitational effects) but we can't actually see it (though there's been a few hints of annihilations that might be consistent with something like a sterile neutrino). It's like looking for a black cat in a coal cellar: we might not see the cat, but we can feel the mice it has killed and (maybe) hear the meow.

If there is a sterile neutrino out there, directly observing it is going to be absurdly hard.

Dark matter is not THEORETICAL. There is direct evidence for it. Quoting from the relevant wiki:

The most direct observational evidence to date for dark matter is in a system known as the Bullet Cluster. In most regions of the universe, dark matter and visible material are found together,[33] as expected because of their mutual gravitational attraction. In the Bullet Cluster, a collision between two galaxy clusters appears to have caused a separation of dark matter and baryonic matter. X-ray observations show that much of the baryonic matter (in the form of 107–108 Kelvin[34] gas, or plasma) in the system is concentrated in the center of the system. Electromagnetic interactions between passing gas particles caused them to slow down and settle near the point of impact. However, weak gravitational lensing observations of the same system show that much of the mass resides outside of the central region of baryonic gas.

In other words, gravitational lensing of light waves - which is 100% direct evidence of matter - shows a region where there is matter that is clearly non-baryonic (i.e. does not interact with the electromagnetic field, a.k.a. "dark"). This is not subject to dispute. The question of what, exactly, is dark matter - is indeed still a subject of scientific research. There are, however, a number of super-symmetric theories which posit super-partners for well known particles, the most stable of which turn out to have the exact characteristics we're noting observationally. It is important to note that these theories were not tailored to account for the dark matter, but seem to fit the observational evidence quite well so far. As with all science however, theories are subject to falsification at any times as soon as new evidence comes on the scene.

It isn't obvious that what we are seeing is matter, dark or otherwise, but only that we see an effect that causes lensing as per our theoretical models and methods of observation. Maybe it's some other force field, maybe conditions are different in the part of the universe we observed -- this is far out but not so much compared to something called "dark matter."

Both of you are wrong. Supercomputer modeling and number dowsing have conclusively proven that the perturbation will cause an E.L.E. boloid strike exactly matching the Mayan prophecy of doom on December 23rd, 2012. They knew this sacred knowledge because they could astral travel using advanced alien technology and actually SEE the dark matter vortex waves.

I understand why they're getting a weak signal here on Earth, where most craters will have long since been erased by erosion and surface remodeling. But I'll bet we could get a much stronger signal from the Moon, particularly the far side. Do we have the ability to get dates for craters there from orbiting probes, or is that something we'd have to collect physical samples to do?

I was just about to say, "the return of the Nemesis theory", except that "theory" was always too strong a word for that - "conjecture", perhaps.

The idea was that sub-stellar-mass dark companion of the Sun would pass near enough to the Oort cloud to throw a barrage of comets into the inner solar system every 35 million years or so, and that we're just about due. The name of this object would be "Nemesis". (I think Asimov wove that into the end of one of his last stories,,,)

Or that dark matter actually exists. I've never seen any definitive scientific evidence of the existence of it. Dark matter just seems to be that stuff we use to answer anything we don't quite understand. Big Bang? Dark matter. Quantum physics? Dark matter. Extinction of the dinosaurs? Dark matter. Why is yo mamma so fat? Dark matter.

Some string theorists claim that when a string bends in the 4th dimension it creates the effects of dark matter.

Not to sound like an idiot because I have no physics degree, but if it exists everywhere why isn't it on Earth or anywhere else? Surely in the last billion years since our solar system revolved around the galaxy once we would at least encounter some of it?

We do. There was a good analysis by somebody I read once looking at how much dark matter you'd expect to find in the solar system. It's not much. Space is really big, and dark matter is pretty well spread around. That's why it doesn't perturb the orbits of the planets noticeably. It also interacts with matter very little, so it's hard to detect.

Every reality-motivated explanation begins as a convenient way to to explain something not presently understood. Photoelectric effect not making sense with classical E&M? Hmmm, what if light came in discrete packets.

Dark matter was at the stage you seem to think it's at around 1960: "Hmmm, it would be convenient if there were more mass where we can't see it..." Starting from the Bullet Cluster, we have observed nearly a dozen galactic cluster collisions where the stars and dark matter pass right by/thro

In retrospect, I rather regret not leaping on some bizzare and obscure science topic very early on in my career. With my early knowledge of pop-science and fantasy TV, film, and comic books, I could have made big headways in modern cosmology and theoretical physics by now.

If you look over the past 500 billion years, the geological record shows that there is a mass extinction event roughly every 62 million years. Even though there is some give and take, on that timescale it's almost like clockwork. Since this discovery, scientists of many disciplines have been trying to figure out what could be causing it. While I admit that it could be a cosmic coincidence, if not, then somewhere a culprit is lurking. There are also lesser extinction events every 26 - 35 million years.

Where the 8,000 came from, was the original poster saying that it was 500 billion years old, with mass extinctions every 62 million, which equaled 130 events. The 8,000 was a sarcastic comment regarding the incorrect maths.

I fully understand the current known facts, and the maths.

I was just curious where the 500 billion number came from that 'MichaelDavidCrawford' was making sarcastic replies to.

If you look over the past 500 billion years, the geological record shows that there is a mass extinction event roughly every 62 million years. Even though there is some give and take, on that timescale it's almost like clockwork. Since this discovery, scientists of many disciplines have been trying to figure out what could be causing it.

Computer scientists think about it for about two seconds. Then they mutter "Must be the garbage collector" and go fetch a beer.

I'm not a physicist but every description I've heard of dark matter more or less boils down to "we've noticed there is more gravity in areas where we don't see mass. And since only mass can generate gravity we have missing mass. We're going to call that missing mass dark matter."

Okay... fine... but that's entirely theoretical. No one has actually found dark matter... as in put it under a microscope or touched it. So... until then, lets not come up with any halfassed theories regarding it.

It would seem to follow that dark matter would tend to naturally form some type of structure. Normal matter certainly forms rather consistent shapes on many different scales. What shapes would dark matter favor if it only interacts gravitationally? Wouldn't it form either a dense ball at the bottom of our galactic gravity well, or flatten into a disc with the rest of the matter in our galaxy? I don't think I've ever read any real theories on it.

I believe this is real. It's on one of those other god like astro physics levels of things, that people don't understand. Like mind control, and directed-energy weapons. People don't understand shit about the universe, how cold it is, or how fucking dangerous and volatile it is..

I think we should ditch planet earth now and focus on building an artificial planetary system which can avoid other planets, comets, energy, and other uncontrollable systems. Immediately, as soon as we can, before we ourselves pari

"So what if there was this giant swarm of space bees, and every 35 million years our solar system–""Wait. Wait, hold on. You're suggesting space bees killed the dinosaurs?""Not directly! These bees are huge. Moon-sized. And they live in the interstellar gaps between stars. I calculated that if their swarm passes through the Oort Cloud, they would get really upset and buzz around, and their gravitational forces would fling asteroids and comets into the solar system.""How did you calculate that the Oort Cloud makes your hypothetical space bees angry?""Well it's a lot more plausible than your hypothetical invisible aether making the sun go wonky."

There's a flaw I see here. When the solar system was formed, chunks of stuff flew around in random directions and collided and there's X chance that one hits Earth. So something comes along and alters the trajectory/orbits of some of this stuff, also randomly. The probability that one hits Earth does not go up. You took something random and made it differently random. For this to be true, the vast majority of matter would regularly have to have magically been specifically not on a trajectory to eventua

Which Dinosaur? There were lots of sizes! I need to quantify this immediately or my brain will turn into dark matter! Get it? Grey matter, dark matter...Laugh or I'll turn this solar system around and we'll go right back to the dark matter.

Dark matter is like the UFOs of astronomy. It's only called "dark" because they don't know what it is yet! UFOs are only "unidentified" until they identify the flying object. There's no reason to think that "dark matter" is something mysterious or alien, astronomers just can't see it...because it doesn't glow!